Conditioned Pain Modulation in Painful Temporomandibular Disorders

Objectives: The influence of descending pain inhibitory system in temporomandibular disorders (TMD) is poorly understood and controversial. The aim of this study was to verify whether conditioned pain modulation (CPM) differs between women with masticatory myofascial (MMF) pain patients and healthy participants.
Methods: Twenty MMF pain patients and 20 healthy participants (control group) were enrolled in this study. The CPM paradigm was performed according to the following: a) pressure pain threshold (PPT) and wind up ratio (WUR) of anterior temporalis was the test stimulus (TS); b) immersion of the participant’s hand up to the wrist in hot water bath maintained at 45.5 – 46.5oC for 1 min was the conditioning stimulus (CS). The TS was assessed before and during the last 30 seconds of the CS (parallel protocol). Pain inhibition along the protocol was represented by a negative value. Thus, the absolute differences between ‘TS before CS’ and ‘TS after CS’ were considered the CPM values. T test for independent samples was applied to the data.
Results: The mean age (SD) of the MMF pain group was 34.6 (9.4) and 30.2 (7.7) for the control group. The absolute CPM mean (SD) was -0.25 (0.2) and -0.3 (0.64) for the MMF pain patients and -1.03 (0.6) and -0.9 (1.3) for the controls considering, respectively, the PPT and WUR as the TS. Between-group difference for the CPM was presented only when the PPT was the TS (p<0.001).
Conclusions: These findings indicate that CPM is less effective in TMD pain patients compared with healthy participants and that threshold measurements, i.e., PPT might be better than rating data, i.e., WUR, to estimate the pain modulation capacity.